Design, Synthesis, and Antifungal Activity of Sulfoximine Derivatives Containing Nitroguanidine Moieties

To discover novel pesticide candidates, a series of sulfoximine derivatives were designed and synthesized via the oxidation coupling reaction of sulfides and N-alkyl nitroguanidines. The compounds were evaluated for their antifungal activity against six phytopathogenic fungi. Most of them exhibited a broad spectrum of fungicidal activity in vitro. Compound 8IV-b displayed good fungicidal activity against Sclerotinia sclerotiorum, Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, and Phytophthora capsici, with EC₅₀ value of 12.82, 12.50, 17.25, 31.08, and 30.11 mg/L, respectively. In addition, compounds 8III-c and 8IV-e had EC₅₀ values of 22.23 and 20.67 mg/L against P. capsic, which were significantly better than that of the commercial procymidone (118.15 mg/L). Strikingly, 8IV-d exhibited satisfactory fungicidal activity against B. cinerea, which was comparable to control procymidone in terms of their EC₅₀ values (7.42 versus 10.83 mg/L), and the bioassays in vivo further confirmed that 8IV-d possessed potent protective effect against B. cinerea at 200 mg/L (72.2 %). These present findings will facilitate the design and development of novel potent fungicides.